Numerous methods have been employed for busing power in electronic systems from a power supply to printed circuit boards.
Wires/Cables. One method has been to communicate power from the power supply to the printed circuit boards by means of discrete wires or cables. Although this method may be desirable for use in relatively low-current systems, large-current systems require wires or cables having large diameters so that the resistive and inductive characteristics of the wires or cables do not unacceptably degrade power delivery performance. Large-diameter wires and cables are problematic because they are stiff, and therefore pose routing difficulties. In addition, large-diameter cables require bulky and expensive connectors at the points of engagement between the wire or cable and the power supply or printed circuit boards. Moreover, large-diameter wires and cables degrade the ability to access other components of a system housed within the same chassis; often, such wires or cables must be removed before access to other components is possible.
Laminated Foil Straps. Another method has been to communicate power by means of straps formed with laminated copper foil layers, often with one lug on each end for engagement with the power supply or printed circuit board. One advantage of such laminated foil straps is that they have fairly good resistive and inductive characteristics even when carrying fairly large currents, and they are more flexible than wires or cables. A major disadvantage of laminated foil straps is that they are very expensive.
Traditional Bus Bars. Still another method has been to utilize rigid copper bars called "bus bars" to communicate power from one point to another within an enclosure. Among the advantages of traditional bus bars are their superior resistive and inductive characteristics and their relatively low cost. The disadvantages associated with traditional bus bars, however, are numerous: First, their rigidity creates difficulties in assembling the electronic systems that employ them. These assembly difficulties are especially apparent with regard to the tolerances they require and to the limitations they place on circuit board orientation choices. (Tolerances must be tightly maintained both in locating the bus bars within the chassis and in mounting the printed circuit boards to the chassis; otherwise, the points of engagement at either end of the bus bars will not be properly aligned with their corresponding mating points.)
Second, traditional bus bars present assembly difficulties in terms of making reliable electrical contacts at each bus bar's points of engagement. Usually, it is necessary during the assembly of such systems to use fastening tools that are capable of applying precisely measurable torque to the bolts being used to attach each bus bar to its mating point, thus insuring good electrical contact. But such tools are expensive, and are often unavailable in the field.
Third, traditional bus bars have either been coated with a layer of some kind of insulating material, or have been left exposed without insulation. Insulating the bus bars adds to the expense of the system, and leaving the bars exposed creates possible shock and short circuit hazards.
It is therefore an object of the invention to provide a bus bar system that facilitates flexibility in circuit board orientation while easing the tolerance requirements presented by prior art bus bar systems.
It is a further object of the invention to provide a bus bar system that makes reliable electrical contacts during assembly without the use of precision fastening tools.
It is yet a further object of the invention to provide a bus bar system that is less expensive to manufacture than systems utilizing insulation-covered bus bars, but that still reduces shock and hazard risks relative to systems utilizing exposed bus bars.